backup: drop BackupHeader loading code

It is useless here since backup restore is moved to
qubes-core-admin-client.

qubes/backup.py

@@ -78,6 +78,7 @@ class BackupHeader(object):
     '''Structure describing backup-header file included as the first file in
     backup archive
     '''
+    # pylint: disable=too-few-public-methods
     header_keys = {
         'version': 'version',
         'encrypted': 'encrypted',
@@ -91,7 +92,6 @@ class BackupHeader(object):
     int_options = ['version']
 
     def __init__(self,
-            header_data=None,
             version=None,
             encrypted=None,
             compressed=None,
@@ -110,67 +110,6 @@ class BackupHeader(object):
         self.crypto_algorithm = crypto_algorithm
         self.backup_id = backup_id
 
-        if header_data is not None:
-            self.load(header_data)
-
-    def load(self, untrusted_header_text):
-        """Parse backup header file.
-
-        :param untrusted_header_text: header content
-        :type untrusted_header_text: basestring
-
-        .. warning::
-            This function may be exposed to not yet verified header,
-            so is security critical.
-        """
-        try:
-            untrusted_header_text = untrusted_header_text.decode('ascii')
-        except UnicodeDecodeError:
-            raise qubes.exc.QubesException(
-                "Non-ASCII characters in backup header")
-        for untrusted_line in untrusted_header_text.splitlines():
-            if untrusted_line.count('=') != 1:
-                raise qubes.exc.QubesException("Invalid backup header")
-            key, value = untrusted_line.strip().split('=', 1)
-            if not _re_alphanum.match(key):
-                raise qubes.exc.QubesException("Invalid backup header (key)")
-            if key not in self.header_keys.keys():
-                # Ignoring unknown option
-                continue
-            if not _re_alphanum.match(value):
-                raise qubes.exc.QubesException("Invalid backup header (value)")
-            if getattr(self, self.header_keys[key]) is not None:
-                raise qubes.exc.QubesException(
-                    "Duplicated header line: {}".format(key))
-            if key in self.bool_options:
-                value = value.lower() in ["1", "true", "yes"]
-            elif key in self.int_options:
-                value = int(value)
-            setattr(self, self.header_keys[key], value)
-
-        self.validate()
-
-    def validate(self):
-        if self.version == 1:
-            # header not really present
-            pass
-        elif self.version in [2, 3, 4]:
-            expected_attrs = ['version', 'encrypted', 'compressed',
-                'hmac_algorithm']
-            if self.encrypted:
-                expected_attrs += ['crypto_algorithm']
-            if self.version >= 3 and self.compressed:
-                expected_attrs += ['compression_filter']
-            if self.version >= 4:
-                expected_attrs += ['backup_id']
-            for key in expected_attrs:
-                if getattr(self, key) is None:
-                    raise qubes.exc.QubesException(
-                        "Backup header lack '{}' info".format(key))
-        else:
-            raise qubes.exc.QubesException(
-                "Unsupported backup version {}".format(self.version))
-
     def save(self, filename):
         with open(filename, "w") as f_header:
             # make sure 'version' is the first key